Dilation instruments are used, inter alia, in endoscopic ENT surgery, but also in other specialist areas of medicine. They are used to remove pathological stenoses by virtue of an expandable section being introduced into the region of the stenosis and the section being dilated. A simple solution for dilation lies in use of a balloon catheter which is disadvantageous if the balloon bursts and “pumping work” is required by the operator if a gas is used. If use is made of an incompressible fluid, the biocompatibility thereof, in turn, needs to be taken into account. Purely mechanical dilation instruments are also known; although these usually cannot be dilated in an ideal manner, they do permit sensitive force feedback with fewer hand movements. Mechanical dilation instruments are often disadvantageous in that comparatively large gaps are formed between the spreading jaws in the spread state, which contributes to an increased risk of trauma due to a pressure load which is too high and due to clamping. As a result of this, overcoats were developed for mechanical dilation instruments, which overcoats are intended to compensate these gaps, homogenize the introduction of force into the tissue and prevent the ingress of tissue into the dilation mechanism.
A dilation instrument with such an overcoat and a method and a device for applying the overcoat have been disclosed in EP 2 412 315 A2. There, the overcoat is held in the device and dilated at the proximal end of said overcoat. The device has a conical insertion aid for the expandable end of the dilation instrument such that it can be introduced into the overcoat more easily. There, the overcoat merely extends over the expandable section in which the dilation mechanism is also arranged. When the dilation mechanism is actuated, the overcoat may inadvertently slip off the expandable end.